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Unhexquadium
Unhexquadrium, Uhq, is the temporary name of element 164. NUCLEAR Proton shell closure has been widely predicted to occur at Z = 164. Among the isotopes of Uhq are at least two, and possibly as many as four doubly-magic nuclides. At least one set of theoretical values for half-lives and decay modes of Uhq have been constructed for neutron count up to N = 333(1). It predicts isotopes in a band ranging from Uhq 435 to Uhq 484. Examination of pp 15 & 18 of Ref. 1 indicates that Uhq 435 through Uhq 452 have sub-microsecond half-lives and decay by fission, including a band from Uhq 436 to Uhq 448 which don’t live long enough to be nuclei. Uhq 453 to Uhq 461 have sub-millisecond half-lives and decay mainly by alpha emission. Uhq 462 to Uhq 484 apparently decay by alpha emission and have half-lives ranging up to around 1 sec. (Values aren’t available for nuclides marked as beta-stable.) Note that isotopes between Uhq 474 and Uhq 484 do not have short half-lives. Beyond Uhq 484 the model appears to indicate a band of short-lived, fission-decaying drops, only a few of which can be considered isotopes of Uhq. These predictions are to be expected for neutron shell closure at N = 308 and a closed proton shell at Z = 164. Doubly-magic Uhq 472 anchors a what has been called the “second island of stability”. What Ref. 1 can’t do is describe heavy isotopes of Uhq. It is possible to use a first-order, liquid-drop approach to guess at the amount of structural correction energy needed to allow a drop of nuclear matter to survive for the 10^-14 sec needed for electromagnetic interactions (such as binding an electron) to become important. At least two computations of the neutron dripline’s location up to Z = 175 exist(2),(3), and since they give similar results, the maximum possible size of a Uhq nucleus can be set slightly above the values computed, allowing only a small margin for error. This gives Uhq 586 as the heaviest possible Uhq isotope. Structural correction required for Uhq 586 itself is around 0.25 MeV, which means all Uhq drops will fission quickly without structural stabilization, but also that sufficient correction is likely. In general, it is not possible to describe structural correction energy. What can be predicted are neutron and proton shell closures, for which correction energy is expected to be particularly large. Neutron shell closures have been predicted at N = 406(3),(4), 370(3), 318(5), and 308(1). The isotope Uhq 570 requires around 1 MeV of structural correction, which means isotopes in the Uhq 560 to Uhq 575 band are highly likely. The isotope Uhq 570 anchors an island in which fission is suppressed enough for beta decay to take place near the neutron dripline (See “Formation” for additional significance of these nuclei.) Uhq 534 requires around 1.5 MeV of structural correction, which means isotopes in the band Uhq 524 to Uhq 539 are also likely. Uhq 534 is a possible doubly-magic nucleus. All isotopes in both bands should beta-decay with half-lives under a second. On the other hand, Uhq 482 requires around 2 MeV of correction energy, which means alpha-decaying nuclei are likely in the band Uhq 472 to Uhq 487. Uhq 482 has been predicted to be doubly magic, but Ref. 1 does not show a pattern of nuclides which indicate a shell closure at N = 318. ATOMIC Several predictions for the ground state electron structure of Uhq agree that it will have transition metal character, with 7d electrons available for bonding. Electrons in Uhq can be described in terms of time-independent orbitals, but calculation of electron properties require that nuclear charge be distributed over the nucleus' actual volume. In addition, there is some chance that differing nuclear shapes may produce different electron configurations in different isotopes. (Different isotopes would be different elements in the chemical sense.) Except in the laboratory, Uhq is expected to exist only in environments too hot for ordinary chemistry to occur. FORMATION Ions of this element may form when material from roughly 1 km depth is ejected from a disintegrating neutron star during a merger. There is a possibility that beta decay from dripline nuclides stabilized by the N = 406 closure, enhanced by the Z = 164 proton shell closure, will allow some isotopes in the vicinity of Uhq 559 to Uhq 577 to form in quantity during such a merger. It improbable that nuclides between Uhq 524 and Uhq 539, or lighter, can form in this way. Fusion or multinucleon transfer reactions in the polar jets emanating from a neutron star or black hole might produce lighter isotopes, including those in the Uhq 435 to Uhq 484 band. Quantities produced by this method are very small. REFERENCES 1. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 2. "Neutron and Proton Drip Lines Using the Modified Bethe-Weizsacker Mass Formula; D.N. Basu et al; Int.J.Mod.Phys.; arXiv:nucl-th/0306061; url: https://arxiv.org/abs/nucl-th/0306061 3. “Single Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region”; H. Koura and S. Chiba; Journal of the Physical Society of Japan; DOI 10.7566/JPSJ.82.014201; Jan. 2013. 4. "Magic Numbers of Ultraheavy Nuclei"; V. Yu Denisov; Physics of Atomic Nuclei, v. 68, no. 7, pp 1133-1137; 2005. 5. “The Highest Limiting Z in the Extended Periodic Table”; Y.K. Gambhir, A. Bhagwat, and M. Gupta; Journal of Physics G: Nuclear and Particle Physics. 42 (12): 125105. DOI:10.1088/0954 3899/42/12/ 125105. (12-13-19)